In many techniques for attacking portable data carriers the normal program run is disturbed by external influences. Interferences of this type can be caused in particular by voltage pulses, the effect of heat or cold, electrical or magnetic fields, electromagnetic waves or particle radiation. For example it is possible to manipulate register contents in the processor core by light flashes on the exposed semiconductor chip of the portable data carrier. The program counter can potentially be modified by such a light attack to make the portable data carrier emit confidential data from an input/output buffer contrary to the programming stored in it.
A device for controlling a door lock motor in a vehicle is known from European patent application EP 1 056 012 A2 in which a control processor executes a plurality of sub-programs one after the other, a counter being incremented after each sub-program. After execution of the sub-programs a check is made as to whether the counter status corresponds to the number of sub-programs.
However, this known device relates only to a system permanently installed in the vehicle. A more general use, in particular in a portable data carrier, is not considered. Moreover, only a strictly sequential sequence of all sub-programs is provided in this device. The teaching known from EP 1 056 012 A2 is therefore not suitable for more complex applications, in which individual sub-programs are optionally to be skipped.